Photographic sound recorder



July 14, 1942- l.. T. AsAczH'l-LJEBEN 2,289,885

PHOTOGRAPHIC SOUND RECORDER Filed April 4, 1940 @emr/wv aF .arman/MQW frm ,vez n Smaentor Patented July 14, 1942 UNITED, STATES PATENTl OFFICE PHo'roGRAPHIC soUNn RECORDER Lawrence T. Sachtleben, Camden, N. J., assignor to Radio Corporation of America, -a corporation of Delaware Application April 4, 1940, Serial No. 327,759

14 Claims.

This invention relates to photographic sound recording and more particularly to the monitoring of the recorded signals' during the recording operation.

The photographic recording of sound on film is well known and Widely used commercially. Although the present invention is described in conjunction with one specic form of recording apparatus, it is apparent that its use is not limited to that specific type of apparatus but 4it may be used with any usual form of photographic sound recorder. In photographic recording of sound it is sometimes desirable for one reason or another to use light of some specific characteristic. For example, it may be desired to use polarized light in order to decrease the rellection of light by the crystals `of sensitive material within the photo-,

graphic emulsion which produces a consequent diifusion of the image.. The recording of sound by polarized light is per se well known, since the light is necessarily polarized in such an appairatus as a Kerr cell recorder. The use of a polarlzer also decreases the intensity of therecording beam some 50 percent and although the monitoring of such a polarized beam is quite practical, as described and claimed, for example,

in Zworykin Patent No. 1,834,197, nevertheless such monitoring causes a further loss of light which is disadvantageous.

In the apparatus of the present invention I provide means for recording with polarized light and for monitoring while recording without reducing the intensity of the recording .beam by removing therefrom the light used for monitoring.r

This result is accomplished by using a light dividing means, such as a. polarizing prism, which will transmit the desired portion of the light beam and which will refract or reflect-the portion of the light beam which is not to be used for recording into the monitoring apparatus where it will serve for monitoring'as effectively as would av portion of the recording beam. It will thus be seen that by usingtheportion of the light beam which would otherwise be discarded, I secure improved -optical efficiency and am enabled to record withlower light intensi-y ties than would otherwise be necessary for securing a record of adequate density.

One object of the invention is to provide an improved photographic sound, recording system.

Another object-of the invention `is to provide f film Yby means a system for recording sound on of polarized light. v Another object of the invention is to provide an improved monitoring system for a photographic sound recorder.

Another object of the invention is to provide a monitoring system which will serve to monitor the recording apparatus by means of the portion of the light beam which would otherwise be discarded. l

Another object of the invention is to provide an improved polarizing and monitoring systen'A which may be attached bodily to a standard sound recording apparatus without anyother Amaterial modiiication thereof.

the prism angles and the angle of the deviated rays in a prism such as shown in Fig. 2.

Referring to the recording apparatus shown in Fig. 1, light from a source lo is directed by the condenser lens II through the aperture in the plate I2 to a second lens I3, whichk with the lens II, focuses an image ofthe light source I0 on the galvanometr mirror I4. The galvanometer mirror I4 is adapted to be vibrated about a horizontal axis and to move the light beam lup and down on the slit plate I1 on which an image of the aperture in the plate I2 is formed by the lenses I3 and I5. A color screen I6 may be inserted, if desired, in front of the slit I8 in the plate II. Light passing through the slit I8 is focused on the lm F by the objective' composed of thelenses 2l and 22.

Adjacent lthe slit I8 there is provided the polarizing prism I9 which will be hereinafter described in more detail. This prism polarizes the light ina predetermined plane without deect.

ing the main polarized beam and it therefore does not interfere with the alignment of the remalning elements'of the opticalsystem. Since the shapeland location of'the prism I9 is determined bythe vposition of the slit I8 a plane par- -llel quartzplate 20 may be placed inthe beam to rotate the plane ofhpolarization of the beam,

if so desired. This plane parallel quartz plate 20 is out with its optic axis parallel to the optical faces thereof are perpendicular to the axis of the ordinary ray, and also in that the prism is of relatively small dimensions along the optithe minimum defocusing of the optical system and renders its addition in a conventional optical system much simpler than would be the ,case with other types of polarizing prisms. An.-

other advantage of this type of prism is that it can be made relatively long and narrow transversely of the beam, which is extremely diiicult in the case of a Nicol prism.

As shown in Fig. 2, the ordinary ray passes.

' through the prism without deflection along the optical axis of the system. The direction of deilection ofthe extraordinary ray depends upon the material of'which the prism is made, the direction of deflection being indicated in Fig. 2 and the quantity thereof as determined by the |angle of the interface of the prism being shown in Fig. 3. It will be apparent from Fig. 2 that 'the extraordinary ray is deflected in one direction for a negative crystal, such as calcite, and in the opposite direction for a positive crystal,

'such as quartz, and the prism would be turned in the appropriate direction according to the material from which it is made.

Referring again to Fig. 1, the extraordinary ray deflected by the prism I9 is directed to the reflector 24 which Ais spaced from the axis of the ordinary ray used for recording a suilicient distance so as to not interfere with-the light transmission through the lenses 2| and 22. This reflector 24 directs the light from the extraordinary ray downward through the lenses 25 to the monitoring device 26, which is here indicated as a photocell. It will be apparent that any other type of monitoring device may be substituted for the photocell. For example, the light may be focused on amonitoring card or a ground glass screen, or the beam may be viewed lthrough an eye piece, if desired.

It will be apparent tol those skilled in the art that my 'invention is not limited to the use of polarized light nor to the use of the specific type of polarizing means described, but that I may substitute other types of light selecting and de- 'flecting means which will transmit the component of the light beam which it is desired to use for recording substantially unchanged while directing the portion of the beam which is not to be used or which is useless for recording to the monitoring apparatus. As an example of such an alternative form of apparatus, the prism I9 may have an interface angle of 45 and have a dichroic reflector such as gold, silver or eosin between the faces. lWith such an arrangement, the reecting interface would, of course, substitute for the reflector 24 and-itself direct the light beam through the lenses 25. The dichroic reilectors mentioned are themselves lwell known and have the following characteristics: eosin 'transmits red and reflects green; gold transmits green and the adjacent portion of the visible spectrum toward the blue and reflects from thev orange into the infra red;,and silver transmits from the blue-violet to the ultra-violet, reflecting the remainder of the visible spectrum.

cai axis. This type of prism, therefore, produces l and for simultaneously defiecting an undesired i ycomponent of said beam, and monitoring means I claim as my invention:

1. Sound recording apparatus for recording the sound by means of a component of a beam of light including means for transmitting said component and for simultaneously deflecting the complementary polarized component of said beam, and monitoring means located in the path of said complementary polarized component.

2. Sound recording apparatus .for recording the sound by means 'of a colored component of a beam of light including means for transmitting said'component and for simultaneously relatively deecting the complementary component of said beam, and monitoring means located in the path of said complementarily colored com- Y ponent.

3. Sound recording apparatus for recording the sound by means of a desired component of a beam of light including polarizing means for transmitting said component and for simultaneously relatively deflecting an undesired component of said beam, and monitoring means located in the path of said undesired component.

4. Sound recording apparatus for recording the sound by means of a component of a beam of light including means for transmitting said component without deflection and for simultaneously deecting the complementary polarized component of saidbeam, and monitoring 'means located in the path of said complementary polarized component.

5. Sound recording l apparatus for recording the sound by means of a desired component of a beam of light including 'polarizing means for transmitting said component without deflection located in the path of said undesired component.

6. Sound recording apparatus including a light source, a light modulator, means for directing modulated light on to a film, and means between said modulator and said film for transmitting one component of the light to the film and relatively deecting the complementary polarized component.

7. Sound recording apparatus including a light source, a light modulator, means for directing modulated light onto a film, means between said modulator and said lm for transmitting a component of the light to the film and relatively deecting the complementary polarized component, and monitoring means in the path of complementary polarized component. Y

8. Sound recording apparatus including a light source, a light modulator, means for directing -modulated light on to a film, and dichroic revfleeting means between said modulator and said fllm for transmitting a desired component of the light and deecting an undesired component.

9. Sound recording apparatus including a light source, a light modulator, means for directing modulated light on to a film, dichroic reflecting means between said modulator and said film for transmitting a desired component of the light and deflecting an undesired component, and monitoring means in the path of said undesired component. Y

, 1 0. Sound recording' apparatus including means for producing a beam of modulated light, means for dividing said beam of light into two portions of qualitatively complementary physical characteristics of which one portion is particularly adapted to recording sound on film, means for,` directing said portion on to a film, and monitoring means in the path of 4said other portion.'

11. In combination with a sound recording systemincluding a narrow aperture adapted to pass a beam of light and means for focusing an image of the light passing through said aperture on to a photographic recording medium, a polarizing prism placed adjacent said aperture and passing the beam of polarized recording light, light deflecting means located in the beam of polarizedk `light not transmitted to said recording medium,

the beam of polarized recording light without, `material deflection, light deecting means located in the beam of polarized light not transmitted to said recording medium, and a. monitoring means located in the deflected beam of light.

13. Sound recording apparatus for recording the sound by means of a desired component of a beam of light including polarizing means for transmitting said component and for simultaneously deiiecting an undesired component of .said beam, monitoringmeans located in the path of said undesired component, and means for rotatf ing the plane of polarization located between the polarizing means and the record.

14. Sound recording apparatus for recording y the sound by means of a desired component of a beam of light including polarizing means forl transmitting said component and for simultaneously deecting an undesired component of' said beam, monitoringmeans located in the path of said undesired component, and means for rotating the plane of polarization located between the polarizing means and the record medium.

LAWRENCE T. SKACHTLEBEN. 

